Water Treatment Plant – Site Development and Stormwater Management

FOX began the planning phase for the Ames Water Treatment Plant (WTP) in 2008. An analysis of the city’s facilities showed that a new, larger facility was needed to meet future water demands. For the new site, Ames selected a 43-acre property that would make use of existing infrastructure. Improvements were made to approximately 19 acres of the property to meet the city’s needs for incorporation of green infrastructure.

Site Overview Aerial Image

Solution:

Extensive utility infrastructure was required to be delivered to the site to meet the demands of the new water plant facility including connections to the city’s finished and raw water system. Project costs were reduced through reuse of and improvements to the city’s existing lime ponds and the ground storage tank at the existing water plant; to allow for this, utility lines were installed between the two locations. This translates to over 13,500 LF of 24-inch finished water line, 6,575 LF of 24-inch raw water line, 5,800 LF of communications conduit, and 4,700 LF of lime sludge delivery lines.

Significant effort was undertaken to limit the impacts of the development while fully utilizing the space available to complement the building program for the new facility. The site layout incorporated much of the open space utilized by the previous owner, thereby limiting disturbance of native grasses and over 25 acres of forested property adjoining the Skunk River.

Site design elements helped to meet Leadership in Energy and Environmental Design (LEED) certification, and included installation of white concrete to reduce the heat island effects of hard surfaces, alternative transportation to the site by incorporating bike racks and low-emitting and fuel-efficient vehicle parking spaces, limiting parking capacity to only the necessary requirements, protecting and restoring habitat in and around the site development, maximizing open space in the developed area, installing stormwater management that will provide water quality treatment to site stormwater runoff, and the use of native landscaping to reduce water use. The layout includes additional parking that allows the administrative areas to be used for training purposes.

Water Treatment Plant Building

Stormwater management has an essential purpose: manage surface water runoff, and prevent ill effects from development downstream. This is vital in urban areas where the ground surface is not permeable, and infiltration is reduced. Highly developed areas have impervious surfaces, such as pavement and roofs, that prevent precipitation from naturally soaking into the ground. Instead, water runs away from these surfaces into storm drains, storm sewers, and drainage channels, sometimes at a high rate of flow. This can cause downstream flooding, stream bank erosion, increased turbidity, habitat destruction, and even damaged infrastructure or contaminated water bodies in extreme cases.

Traditional stormwater management generally includes restricting the peak flows from a development to match the flows prior to development. Unfortunately, this does not mitigate the volume of water that is produced from the increase in impervious areas and only dislocates high water loads. Modern approaches require that the natural water cycle be rebuilt to allow stormwater runoff to infiltrate and recharge the groundwater where possible.

Bioretention Cell Plantings

Green infrastructure, often referred to in stormwater management as Low Impact Development, generally includes approaches and technologies to reduce the impacts of development by promoting infiltration, evapotranspiration, and capture/reuse of stormwater to maintain or restore the natural hydrology in the environment.

FOX completed a site design that incorporates a variety of green infrastructure stormwater practices. This includes an extended detention facility to meet the required stormwater site discharge requirements, two bioretention facilities to provide water quality treatment of runoff from impervious parking areas, a bioswale to treat runoff from the city’s maintenance area, grass swales to promote infiltration in drainage channels, and restoration of habitat to native plantings to further reduce runoff.

Bioretention Cell in Parking Areas

Locations were chosen because they provide a “treatment train” of practices to reduce runoff and promote infiltration prior to discharge from the site. By including over 10 acres of native grass seeding within the 19-acre development, the facility improvements can return a large portion of the development back to a native landscape.

Benefits:

Site development for the new Ames Water Treatment Plant provides the needed elements to allow operation of the facility for many years. Incorporation of stormwater management practices into development of the site greatly reduces the stormwater runoff and provides water quality treatment from impervious areas.

Incorporating these water quality practices greatly enhances the facility, and provides an opportunity for the city to demonstrate the benefits of these practices – ensuring clean water for future generations.